I have checked our mail log and don't actually see any errors. Is there any way for me to find out what is going on and sort of investigate this further using any tools or something to make sure that our mailserver are working fine. At this point, we are just pointing blame to each other's mailserver.

A different question. If we were to create a new mailserver, is there an easy way to migrate all the users and emails from our old mailserver to the new mailserver? FYI, the current mailserver is setup using the guide in this site, ie. "Virtual Users With Postfix, PostfixAdmin, Courier, Mailscanner, ClamAV On CentOS". However, the current mailserver is running on FC5.

Basically what happened was that whenever the remote mailserver tried to connect to the local mailserver, there was a RBL lookup error. This only happens with opm.blitzed.org and sbl-xbl.spamhaus.org.

Because of that RBL lookup error, the connection was terminated. I have removed the 2 RBL server from main.cf. As far as I know from surfing the net, opm.blitzed.org is no longer active, while spamhaus.org have changed it to zen.spamhaus.org. However, I am still getting RBL lookup error with zen.spamhaus.org, so I have removed that from main.cf too.

Anyone have these RBL lookup errors with zen.spamhaus.org? What causes this lookup errors and is there any alternative spamhaus server that I can use that won't cause these RBL lookup errors.

I don't think the IP of the remote server is blacklisted. I've checked against Spamhaus IP Address Lookup on their website and it is not listed.

Why would a blacklisted IP caused a RBL lookup error? How do you use spamhaus's spamfilter server, ie. zen.spamhaus.org? Before I removed that entry from postfix's main.cf. Below is a clip from my main.cf